NAPLES FAUNA IN WESTERN NEW YORK, PART 2 29 I 



Dimensions. An average specimen measures, hight 20 mm, length 

 18 mm. 



Habitat. Genesee province ; Naples subprovince. Occasionally in 

 the shales at Parrish gully, Naples N. Y. Cardiola subarticulata 

 Beush. is from Martenberg, Westphalia. 



Genus Euthydesma Hall. 1885 



Euthydesma was based on the species we are about to notice; and, 

 after careful study of all available material of the genus from the Intu- 

 mescens fauna and comparison with the accounts given by Holzapfel and 

 Beushausen of the shell described as Mytilarca and Euthydesma 

 b e y r i c h i, we are disposed to conclude that at present but one specific 

 type of this genus is known. The New York shells are of considerable, 

 often large size, with umbones full, rotund and anterior and the surface 

 generally characterized by broad and obliquely concentric ridges. The 

 actual attitude of the beaks we are disposed to believe is opisthogyre, 

 though our preparations are not of such character as finally to determine 

 this point. Yet from analogy with Lunulicardium we find much that 

 supports this view ; the posterior cardinal ribs (two to five in number) 

 constitute all the radial plications of the surface and are quite sug- 

 gestive of the posterior plications in Lunulicardium, specially the species 

 L. beushauseni. This similarity to L. beushauseni is somewhat 

 emphasized by such specimens as that figured on our plate 9 [fig. 15], where 

 the shell seems to have a scar of early injury running obliquely forward 

 from the beak, giving the apex an apparently posterior direction and the 

 anterior margin a subtruncate aspect. This phenomenon has been 

 observed in more than one instance and may not prove to be wholly casual. 

 Hall described the hinge line as " rigidly straight " and as bearing a well 

 defined ligamental groove. Our preparations show that the cardinal or 

 ligament area is rather short, moderately high, arched and finely striated 

 horizontally. It is interrupted directly under the beak by a transverse or 

 vertical ridge and corresponding depression, so that this modification of the 



